Space based satellites currently make use of a number of sensing devices which can be used to monitor the satellite's orientation in space, and horizon sensors specifically are used to monitor the rotation of the satellite so as to allow unwanted rotations to be corrected. Such monitoring of the satellite's position and rotation is typically performed by placing a number of sensors along the outer perimeter of the satellite's body. As the satellite rotates in space it will, depending on its particular position, pass through zones of light and shadow as a result of light or infrared radiation.
Currently known sensors for detecting satellite position fall into three main categories, all of which possess certain disadvantages.
Some horizon sensors are implemented using photodiodes. These photodiode based sensors have a radiation detection spectrum which ranges from 0.4 to 0.7 .mu.m in wavelength. These photodiode sensors, however, have proven to be unreliable when used for the duration of service required in space-based satellites. An additional disadvantage to these system is that such photodiodes exhibit a low resistance to harmful ionizing radiation which is commonly encountered in space.
Another common sensor arrangement makes use of thermopiles, usually configured in an array. The thermopiles are used in conjunction with thermocouples and are normally arranged in series. Such a configuration is simple to construct and makes use of a minimum of electronic components, but is possessed of the disadvantage of having a long response time which makes them undesirable for use in critical applications.
Other horizon sensors make use of pyroelectric detectors which contain dielectric materials whose polarization properties change as a function of temperature. Such devices have fast response times but are hampered by low levels of sensitivity which make them undesirable for certain critical satellite positioning applications.
It would therefore be highly advantageous to have a space-based horizon sensor with a fast response time that is also highly sensitive to temperature variation so as to enable its use in critical space-based satellite positioning applications.